I assume you mean the BA49 LHR-SEA. Looking at EF, BA are still showing a reasonable amount of availability across WTP, as well as the other classes:



However, looking at the seat map you can see that whilst WTP appears fully occupied, aside from the bassinet seats, CW is pretty empty at present:


I would assume that you'll either be able to get one of the bassinet seats closer to departure, or BA will be undertaking a number of opups and/or downgrades to accommodate everyone.